So I know that Cylinder #3 is misfire. I just recently replaced the plugs with the autolite iridiums, and the air cleaner. Ran awesome for few days, then it started to have a very rough idle at a stop. I tried to remove the plug, look at it and reinstall it, same issue, same cylinder. So I bought another plug, just to try and see if this fixed the problem, then I was going to check the coils by switching them, plugs were in store, Coils is special order. I first tried the spark plug and surprisingly it fixed the problem. So it must be a bad plug (New one), right? I mean, when a coil goes bad, can it send to much charge to the plug and ruin them? I know this may be a stupid question, but just wanted to ask before I purchase 6 coils, might as well do all if I do them. I have a long trip planne this Sat, so ......
Thanks for your replys

Why would you purchase 6 coils when you only have a single misfire? what i would do is take the number 3 coil and move it to 4, 5 or 6 cyclinder or whichever one and see if the misfire will jump to the other cylinder once the car is running and a cycle being completed. IF the misfire jumps then most likley you have a bad coil.

On an 06 I would probably replace all coils too.....just for peace of mind.

The benefit of coil overs is that when you have a problem like this you can replace just the single coil. The downside is they are generally more expensive if you have to replace the whole set in comparison to a traditional coil pack. However, just because his coils are OE on a 2006 doesn't suggest he should replace the lot. That would honestly be a huge waste of money, albeit you can find them fairly inexpensive some places. For example here you can get them for my e90 sedan for 29.99 a piece. Like the old saying goes, don't fix it if it ain't broke.

I have a 07 335i, 80k miles on it. I don't drive a lot, usually go to work on my bike. Thursday I got the P0303 code as well and car is misfiring. I will order the spark plugs and the coil as well. At 80K miles, should I replace the 1 coil or should I replace them all for peace of mind? Since I'm going to be working on replacing plugs and at least 1 coil, anything else I should replace while I'm working on that?